The invention relates to a circular knitting machine having a first needle bed in the form of a needle cylinder which has grooves for first knitting needles, a first cam for controlling the first knitting needles, a second needle bed in the form of a dial which has grooves for second knitting needles, and a second cam for controlling the second knitting needles, the two needle beds fixing a vertical and a horizontal comb spacing as well as a stitch spacing.
In circular knitting machines of this type (e.g. DE 41 28 372 A1) three dimensions are fixed by the relative position of the needle cylinder and of the dial, these dimensions being described hereinafter as “axial comb spacing”, “radial comb spacing” and “stitch spacing”. The axial comb spacing is given by the spacing between the upper end fare or the stitch knocking-over edge of the needle cylinder and the grounds or bases of the grooves which are formed in the dial and which receive the dial needles, whilst the radial comb spacing is provided by the spacing between the outer end face or the stitch knocking-over edge of the dial and the bases of the grooves which are formed in the needle cylinder and which receive the cylinder needles. The two comb spacings defined in this manner finally fix the dimension described as the stitch spacing (or stitch length), which is substantially produced by the spacing between two circular lines, of which the one is provided by the outer circumferential line of the dial at the level of its groove bases and the other is provided by the outer circumferential line of the needle cylinder at the level of its groove bases.
In the production of knitwear, using both the needle cylinder and the dial, it is frequently desired to select values which deviate from the standard values, particularly large values, for the spacings mentioned, especially the stitch spacing. This applies e.g. in the use of circular knitting machines of the type described initially for the production of so-called “spacer fabrics”. This term is understood to refer to knitted goods which comprise essentially two fabric webs produced solely with the needles of the needle cylinder or respectively solely with the needles of the dial, these fabric webs being inter-connected by thin intermediate layers (e.g. DE 74 25 934 U1, DE 28 50 823 A1). These intermediate layers are formed in that, between the method steps intended for the production of the two fabric webs, a mostly thin, monofil connecting thread is inserted both into the cylinder needles and into the dial needles and is worked by the latter in the manner of tack stitches. The lengths of the sections of this connecting thread which lie between the two fabric webs and thus also the total thickness of the spacer fabric depend substantially on the size of the stitch spacing and are the larger, the further the two above-mentioned circular lines, which define the stitch spacing, are spaced apart from one another.
When standard circular knitting machines having needle cylinders and dials are used, which are suitable also for other purposes, the stitch spacing is comparatively small, since e.g. the axial comb spacing is a maximum of approx. 5.6 mm and the radial comb spacing is a maim of approx. 1 mm. Even in circular knitting machines in which the axial comb spacing is variable by axial displacement of the dial relative to the needle cylinder, as applies also to the above-mentioned known circular knitting es, the maximum axial comb spacing which can be produced is generally less than 6 mm, whilst the radial comb spacing is fixedly predetermined by the external diameter of the needle cylinder and of the dial at a value of approx. 1 mm.
The small size of the maximum axial comb spacing is, inter alia, a consequence of the latch needles usually used and of the small latch lengths or hinge lengths of latch needles. Since namely on the one hand the connecting thread, when being bound into the tuck position, has to be inserted substantially simultaneously both into the cylinder needles and into the dial needles, and on the other hand during thread take-up the cylinder and dial needles may only be raised at a maximum so far that in so doing the (“old”) stitches which are located in their hooks still remain on the open needle latches and do not slide out over the latches onto the needle shafts, the axial comb spacing is substantially limited by the latch length of the knitting needles used. Corresponding limitations arise in respect of the radial comb spacing and in the production of goods other than spacer fabrics.
In connection with the production of spacer fabrics it is already known (US 2002/0152776 A1) to enlarge the stitch spacing by selecting the two comb spacings at least twice as big and preferably three to four times as big as in standard machines. In view of the above explanations, however, this would presuppose that the cylinder needles and/or dial needles can be raised correspondingly far and to this end are provided with correspondingly long latches which despite the increased raising make possible an arrangement of the knitting needles in a tuck position.
The construction of a circular knitting machine taking into account these requirements is possible in principle, but leads to the disadvantage of a comparatively large width of the knitting systems and/or a comparatively low maximum knitting speed. Depending on the speed at which the needle cylinder and the dial are rotated relative to a stationary cylinder cam and dial cam (or the other way round), the raising and take-down curves of the cylinder cam and dial cam may not exceed a pre-selected maximum steepness in order to avoid needle breakages. This inevitably results in a certain minimum width of the individual knitting systems and leads to circular knitting machines which can have, on the circumference of a needle cylinder which has a diameter of 30 inches, at the most approx. 48 knitting systems (approx. 1.6 knitting systems per inch). If for a complete stitch row of a spacer fabric, as is frequently the case, six adjacent knitting systems are required, at the most therefore approx. 8 full stitch rows or sections of knitted fabric can be produced per revolution of the needle cylinder.
It is, therefore, an object of this invention to so design the circular knitting machine of the kind specified above that the disadvantages mentioned above are avoided even if a comparatively large maximum stitch spacing is provided.
Another object underlying this invention is to so design the circular knitting machine mentioned, above that it can be operated with smaller system widths and at higher speeds.
Yet another object of this invention is to provide a circular knitting machine for producing spacer fabrics which machine has a comparatively large maximum stitch spacing and can be operated with smaller system widths and/or at higher speeds.